Previous physiologic air sampling pumps are known in the prior art. A shortcoming associated with such known sampling pumps arises from these pumps varying the pump motor speed to in turn vary the magnitude of air flowing through the sampling medium in an attempt to sample the air in proportion to the inhalation rate of a person being monitored.
As such, existing pumps cannot follow inhalation rapidly due to the transition time inherent in changing pump speed. This sluggish response is exacerbated at the collection medium because of the long (normally 3 foot long) air tube that the change in air flow must propagate through between the collection medium and the pump motor. If either a person's inhalation rate, or contaminant concentration changes quickly, the mass of contaminant collected, and therefore the derived concentration, will not represent an actual inhaled dose.
Moreover, previous physiologic sampling pumps are known which cannot be used to sample the respirable fraction of particulates. Larger non-respirable particles are deposited upon the pump filter and bias the mass being collected unless separated from the air flow upstream, such as which is accomplished by a pre-collector component such as a cyclone. As is further known, pre-collectors exhibit collection efficiencies which are a function of the effective aerodynamic diameters of the particles in the air stream, the inlet air velocity, and associated physical design of the collector body.
Furthermore, a known and constant flow is maintained in traditional sampling pumps during the entire sampling session in order to know the collection efficiency and to calculate respirable concentrations. Known PSPs also are designed that vary pump speed which in turn varies air flow to follow a subject's breathing rate, the effect of which is to vary the inlet air velocity, thereby varying the fractional collection efficiency associated with each particle size over the sampling time, and which largely renders making valid calculations of airborne concentrations of particulates impossible.
As such, and due to the variable sampling rates endemic to known physiologic pumps (such as which can also be termed as personal dust samplers), the problem of size-selective sampling remains unsolved in order to provide effective air contamination monitoring.